1. Field of the Invention
The present invention relates to a three dimensional cold forging method for shaping a hollow article without rough edges and an apparatus for the method, and especially for shaping a thin metallic wall of a blank to be forged, from which a hollow forged art work having a three dimensional shape can be made, and by this method, the strength of the article itself can be enhanced, and more, integrate forging effect wherein seamless or nonrough edge products can be obtained is resulted.
2. Description of the Prior Art
A so-called three dimensional metallic hollow art article means that, the metallic article itself is hollow, while the interior and the exterior walls thereof are both undulated and can be bent randomly in any of the three dimensional directions; the range of raising and depressing (undulating) includes those individual concaved and convex unit walls, and the continuous walls being raised and recessed; the cavities in the unit walls or the continuous walls are communicated with the hollow cavities of the articles; such hollow art works normally are in the shapes of fruits such as grape bunches, star fruits, bananas or balsam pears.
Taking the above stated three dimensional metallic hollow art works as an example, an analysis is done for the cold forging technique in the art and the problems thereof are decribed herebelow:
1) Press forging with a pair of metallic half dies: the cavities of the metallic half dies are provided with separated contact areas, this tends to form on the the surfaces of a workpiece rough edges, and a troublesome polishing after forging is required to eliminate the rough edges, when the contour of the undulated surfaces of the workpiece is overly complicated, it will be very hard to eliminate the rough edges by polishing; if it is desired to form a hollow forged inner wall on the workpiece, a predetermined three dimensional die core must be inserted in the hollow blank in advance, therefore, after press forging of the metallic half dies, the three dimensional die core is unable to be taken out, press forging thus can not be completed. PA1 2) Swaging with drawing force: drawing forging can only be proceeded on the interior and exterior walls with continuous predetermined contours, it can not be proceeded on the walls with independent undulated unit wall decorations. PA1 3) Rotation forging: this is mostly applied on the continuous wall of a blank, it can reach the required three dimensional forging gradually, however, it still can't be applied on the walls with independent undulated unit wall decorations. PA1 1 . Two hollow plastic housings are formed of PET or PVC plastic material and by the vacuum forming technique (such as the forming technique for a PET bottle) and are a hollow die-protecting member and an inner die; this can lower the cost of manufacturing a die having a die cavity without a seam, and also renders the die cavity to be changeable. PA1 2. The space between the die-protecting member and the wall of the inner die without a seam is filled with mercury of higher specific weight or water solution including cured starch used as a freezing medium, the feature that the mercury or the water solution of the starch can be poured and recollected under normal temperatures as well as that they are provided with stiffness after being frozen make them able of supporting the die cavity for resisting the forging pressure after being frozen, and also is favorable to releasing of the shaped workpiece after defreezing, or for changing the inner die, so that the members and the elements can be recollected for reuse. PA1 3. When liquid mercury or water solution of starch is used as a freezing medium, material such as natural iron sand, iron sand or steel beads can be added thereto and mixed therewith depending on the desired compressive strength of the forging die, to increase the strength of the freezing medium. PA1 4. Based on the law of conservation of energy and by the high plasticity of polyurethane, a polyurethane strip can be inserted in a bore of a workpiece to be forged, the strip is used as a medium for expanding outwardly by swaging of a forging press, such a means of swaging renders the inner and the outer walls of the workpiece to be shaped in three dimensions without a seam. PA1 5. By elastic restoring force of the polyurethane, after removing of the forging press, the polyurethane strip can be taken out of the hollow cavity of the shaped workpiece easily, and the contour of the inner wall can be seen.
The above stated conventional forging techniques are hard to be used to make a three dimensional metallic hollow art work, and under the requirement of getting rid of seams and rough edges, such techniques are even more difficult in forging; yet excavation of die cavities in the conventional forging techniques costs overly high, normally, metallic dies are made of the material better than the medium carbon steel or manganese steel or tungsten steel to be coincident with the strength requirement in die forging, and they can only be used for forging a single article, cost of forging can hardly be reduced.
If the scope of variation of the shape of a hollow metallic article resulted from a forging technique is limited not to broadening, or even an industrial product being required for adequate strength is unable of changing to being artistic, improvement in delicacy of an industrial art work meets a big impedence, the goal of promotion of industy in this art is just hard to be attained.